Can you elect to not hit a second target with Geen Flame Blade even if one is in range?
— Roger Giovannangeli (@WrathfulOgre) November 11, 2020
Yesterday the Green-Flame Blade spell received updated wording (link below) that, among other tweaks, clarifies that the spellcaster can choose whether to launch green fire at a second target: https://t.co/sSnpLkq6bV #DnD https://t.co/ac9ooYnOoe
— Jeremy Crawford (@JeremyECrawford) November 11, 2020
You can, but that means sacrificing 62.5% of the damage, and at that point, why are you bothering to use the spell in the first place?
Use a different cantrip, because Green-Flame Blade is simply so suboptimal as to be absurd to use now. It’s the latest “Trap Pick” in the book, and one of the worst.